The analytical relations of parametric peak gain versus fiber nonlinear coefficient and fiber dispersion versus the difference between gain peak and pump wavelengths were derived when the fiber loss was taken into account, based on which a new method to measure the nonlinear coefficient and dispersion parameters was proposed with only simple algebraic calculation required. In the experiment, a 1450-m-long highly nonlinear dispersion flattened fiber (HNLF) was measured by using two different pump wavelengths, the measured nonlinear coefficient was γ=11.8 W-1?km-1, and the dispersion slope was S=0.0157 ps/(nm2?km) with the error from the value given by the manufacturer below 5%. The measured asymmetry of gain spectrum ascribed to the Raman effect was discussed.